There have been great advances in apparatuses for recording and playing back signals on disk-formed recording media (hereinafter called “disk”) such as hard disks and optical disks. For example, the recording density of a hard disk apparatus has been increasing at a rate of close to 100% every year. In order to increase the recording density further in years to come, it is required that the space between the disk surface on which signals are recorded and the head slider on which the head is mounted (i.e., the floating height) be decreased further. More concretely, a stable provision of a floating height below 20 nm is required.
One of the effective ways to stably provide such a micro floating height is to smoothen the disk surface.
As a mechanism for holding the head slider and allowing the same to perform floating operation in a disk drive, the mechanism of a Contact Start Stop (CSS) system is being widely used. The mechanism of the CSS system is such that the head slider is kept in contact with the surface of the disk at rest while the disk rotation is stopped and, when the disk is started to rotate for performing recording and playback, the head slider slides along the disk surface and finally reaches a predetermined floating height over the disk surface. In this floating state, the head mounted on the head slider performs recording or playback. Therefore, when a smooth-surfaced disk is used, the head slider adheres to the disk when the disk is stopped. Once such adhesion occurs, a disk rotating torque overcoming the adhesive force is needed. Hence, the apparatus requires a large driving electric power. If the adhesive force becomes too great, such an event can occur that normal startup becomes impossible. In order to prevent occurrence of such adhesion, bumps and dimps generally called “texture” are provided on the surface of the disk. Then, the head slider must have a floating height at least not causing the head slider to contact the bumps of the texture. Therefore, a floating height smaller than the distance defined by the bumps of the texture is inconceivable and, hence, there is a limit to realization of a lower floating height.
As a method to prevent a head slider from adhering to a smooth-surfaced disk, a mechanism for holding and floating the head slider on a Non-Contact Start Stop (NCSS) system is being considered. The mechanism of this type is such that it allows the head slider to be displaced to a retreat position at a different location from the disk surface while the disk rotation is stopped. When the head slider is caused to operate afloat over the disk, the mechanism works such that the disk is rotated at a predetermined number of revolutions for some time and then the head slider is shifted from the retreat position to over the disk surface to be set afloat.
An example of the described mechanisms is that of a ramp loading type. The mechanism of this type is such that it allows the head slider to be retreated to a retreat position provided by a slope (ramp) at a predetermined location adjacent to the outer edge surface of the disk while the disk rotation is stopped, whereby the head slider is kept out of contact with the disk surface.
In such disk drives, a head slider of a structure making use of both positive pressure and negative pressure is generally used. The head slider of this type is configured to obtain a constant amount of floatage by virtue of equilibrium of three forces as mentioned below. The first of the forces is that of a load due to a suspension acting so as to press the head slider against the disk surface. The second is a positive pressure due to an air flow produced by the disk rotation acting so as to float the head slider. The third is a negative pressure generated by the same air flow but at a recess made in the head slider acting so as to pull the head slider back to the side of the disk.
However, there has been problems as mentioned below in the use of head sliders according to the NCSS system, in which the head slider is pulled up from the disk surface and displaced to a retreat position as, for example, in the ramp loading method. Namely, at the time of unloading, even when the load from the suspension is eliminated, the negative pressure does not immediately decrease because of the existence of the air flow due to the rotation of the disk. Therefore, an extra lifting load to overcome the negative pressure is needed. Further, a greater lifting stroke is needed. This has made it difficult to make the head slider smaller and thinner and to allow it a faster unloading operation. Further, at the time of loading when the head slider is shifted from the retreat position to over the surface of the disk so as to be steadily set afloat, the attitude of the head slider tends to become unstable when it is pulled down toward the disk surface, and sometimes the head slider collides with the surface of the disk to damage it.
To overcome the described problems, a head slider structured so as to quickly decrease the negative pressure at the time of unloading is disclosed in U.S. Pat. No. 6,288,874. FIG. 12A is a plan view of the head slider seen from the face opposing the disk. FIG. 12B is a sectional side view showing the relationship between head slider 3 and disk 2 in the state of head slider 3 being afloat over the outer edge portion of disk 2 before being unloaded. Incidentally, though head slider 3 floats over disk 2 by being supported by a suspension, the suspension is not illustrated in the drawing for simplicity of description. FIG. 12A and FIG. 12B also show positive pressure Fp, negative pressure Fn, and load Fs from the suspension (not shown) as well as their respective points of application of the pressures.
The suspension (not shown) holds head slider 3 through a gimbal (not shown) and applies load Fs to head slider 3 by means of a pivot (not shown) located at point of application Ps. Negative pressure generating section 74 is of a structure surrounded by protruded rail portions on both sides 72, hence having a deep step, or a sharp drop in level, and having an opening at its outlet end. Air inflow from both sides is prevented by rail portions on both sides 72 and thereby the efficiency of generation of negative pressure is enhanced. At the distal ends on the outlet side of rail portions on both sides 72, there are provided closer-to-disk faces 71 which are slightly higher than rail portions on both sides 72, hence closer to disk 2. Head 80 is disposed on one of closer-to-disk faces 71.
Positive pressure generating section 73 is made up of shallow-stepped portion 731 at the same level as rail portions on both sides 72 and inlet-side closer-to-disk face 732 at the same level as closer-to-disk face 71. Between positive pressure generating section 73 and negative pressure generating section 74, there is provided setting region 76 at the same level as rail portions on both sides 72. By adjusting the width (SW) of setting region 76, the point of application of negative pressure Pn is set on the outlet side, i.e., on the down stream side, of the point of application of suspension load Ps.
The transition from the condition of the head slider 3 steadily floating over disk 2 in rotation to the condition of its being unloaded takes place in this way. Namely, when load Fs from the suspension is decreased for the unloading, positive pressure Fp and negative pressure Fn cannot immediately decrease following the decrease of load Fs. Consequently, an angular moment is generated by the two forces and applied to head slider 3. The angular moment acts so as to quickly increase the pitch angle of head slider 3, i.e., the angle formed between head slider 3 and the surface of disk 2. Hence, the gap between inlet-side closer-to-disk face 732 and disk 2 is rapidly increased. As a result, the amount of air flow taken from the inlet side into the space between head slider 3 and disk 2 is increased to quickly decrease negative pressure Fn. Accordingly, adhesion of head slider 3 to disk 2 due to the production of negative pressure at the time of unloading can be suppressed and a stabilized unloading operation can be performed with the ramp at the retreat position kept at a minimum required height.
However, in the described mechanism to increase the pitch angle by making use of the angular moment to thereby decrease the negative pressure, there is a possibility of occurrence of an excessive angular moment, which is applied to head slider 3 to cause head slider 3 to come into contact with disk 2. When, for example, an external shock is applied to the disk drive, while load Fs from the suspension is being decreased for unloading, so that head slider 3 is caused to approach disk 2, then positive pressure Fp increases immediately but negative pressure Fn changes slower than the change of positive pressure Fp. That is, such a state is brought about in which, while load Fs from the suspension is decreased, positive pressure Fp increases and, nevertheless, negative pressure Fn does not change much. In this state, the angular moment applied to head slider 3 becomes greater than usual. Hence, the end of the air outlet side of head slider 3 comes into contact with disk 2 so that head slider 3 or disk 2 sometimes suffers damage.
When power supply to a disk drive is cut off for some reason or other while the apparatus is in operation, it is required that the unloading operation be completed before the rotation of disk 2 is stopped. Also when an unloading operation is performed in such an unstable state with the rotational speed of disk 2 decreased, then, though the positive pressure decreases with the decrease in the air flow velocity, the negative pressure does not decrease keeping pace with the decrease in the positive pressure. Hence, equilibrium of the forces is lost and an angular moment is produced to be applied to head slider 3, so that there arises a possibility of the end of the air outlet side coming into contact with disk 2. When, as in the conventional art example, point of application Pn of negative pressure Fn is set on the downstream side of the point of application Ps of load Fs from the suspension, the pitch-angle rigidity, i.e., degree of stability against change in pitch angle, decreases. Therefore, head slider 3 easily vibrates when subjected to external disturbance such as an impact and, further, the possibility of its coming into contact with disk 2 at the time of unloading increases.
Further, in the loading operation to move the head slider from the retreat position to over the disk surface, it is necessary to allow the head slider, which is supported by a suspension generally made of an elastic member, to be set afloat over the disk surface without being damaged. In the head slider of the ramp loading type as described above, the loading is performed from the ramp portion, and hence a relatively stable floating operation can be realized. However, in the case of such a type on the NCSS system in which the head slider is brought to over the disk surface and, then, set afloat while it is pushed downward, the effect of vibration of the suspension cannot be sufficiently eliminated and a stabilized floating motion is difficult to attain. For example, the pitch angle of the head slider when it is steadily afloat over a disk is generally 0.1 mrad or so. On the other hand, when the suspension vibrates while the head slider is pushed down, the head slider can be loaded over the disk surface at a pitch angle greater than 1 mrad. When such a great pitch angle is produced, the end face of the head slider can come into contact with the disk to cause damage, before a gap to provide a sufficient positive pressure is secured between the positive pressure generating section and the disk.